Audio non-linearity cancellation for switches for audio and other applications

ABSTRACT

An aspect includes an apparatus including a first amplifier; a first field effect transistor (FET) including a first source coupled to an output of the first amplifier, and a first drain for coupling to a first load; and a first gate drive circuit including an input coupled to the output of the first amplifier and an output coupled to a first gate of the first FET. Another aspect includes a method including amplifying a first audio signal using a first audio amplifier to generate a first voltage; generating a first gate voltage based on the first voltage; applying the first gate voltage to a first gate of a first field effect transistor (FET) coupled between the first audio amplifier and a first audio transducer; and applying the first voltage to a first source of the first FET.

FIELD

Aspects of the present disclosure relate generally to signalnon-linearity cancellation, and in particular, to audio non-linearitycancellation for switches for audio and other applications.

BACKGROUND

An integrated circuit (IC) may provide different types of data to one ormore devices connected to a signal port, such as a Universal Serial Bus(USB) port. The devices connected to a USB port, for example, may varysignificantly. Some devices receive high speed USB data (e.g., up to 10Gigabytes per second), and other devices, such as audio devices, receiveaudio data at much lower speeds (e.g., 40 Kilobytes per second). Becauseof the large speed disparity, and common USB port through which the datapropagates, there are many challenges to accommodate different types ofdata.

SUMMARY

The following presents a simplified summary of one or moreimplementations in order to provide a basic understanding of suchimplementations. This summary is not an extensive overview of allcontemplated implementations, and is intended to neither identify key orcritical elements of all implementations nor delineate the scope of anyor all implementations. Its sole purpose is to present some concepts ofone or more implementations in a simplified form as a prelude to themore detailed description that is presented later.

An aspect of the disclosure relates to an apparatus. The apparatusincludes a first amplifier; a first field effect transistor (FET)including a first source coupled to an output of the first amplifier,and a first drain for coupling to a first load; and a first gate drivecircuit including an input coupled to the output of the first amplifierand an output coupled to a first gate of the first FET.

Another aspect of the disclosure relates to a method. The methodincludes amplifying a first audio signal using a first audio amplifierto generate a first voltage; generating a first gate voltage based onthe first voltage; and applying the first gate voltage to a first gateof a first field effect transistor (FET) coupled between the first audioamplifier and a first audio transducer.

Another aspect of the disclosure relates to an apparatus. The apparatusincludes means for amplifying a first audio signal using a first audioamplifier to generate a first voltage; means for generating a first gatevoltage based on the first voltage; and means for applying the firstgate voltage to a first gate of a first field effect transistor (FET)coupled between the first audio amplifier and a first audio transducer.

Another aspect of the disclosure relates to a wireless communicationdevice. The wireless communication device includes at least one antenna;a transceiver coupled to the at least one antenna; at least one digitalsignal processing core coupled to the transceiver; a port configured toconnect to one of at least one audio transducer and a digital datadevice; at least one audio amplifier; at least one field effecttransistor (FET) including a source coupled to an output of the at leastone audio amplifier, respectively, and a drain coupled to the port; andat least one gate drive circuit including an input coupled to the outputof the at least one audio amplifier, and an output coupled to a gate ofthe at least one FET.

To the accomplishment of the foregoing and related ends, the one or moreimplementations include the features hereinafter fully described andparticularly pointed out in the claims. The following description andthe annexed drawings set forth in detail certain illustrative aspects ofthe one or more implementations. These aspects are indicative, however,of but a few of the various ways in which the principles of variousimplementations may be employed and the description implementations areintended to include all such aspects and their equivalents.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a block/schematic diagram of an example apparatus fortransmitting different types of data via one or more common nodes inaccordance with an aspect of the disclosure.

FIG. 2 illustrates a block/schematic diagram of another exampleapparatus for transmitting different types of data via one or morecommon nodes in accordance with another aspect of the disclosure.

FIG. 3 illustrates a schematic diagram of an example apparatus fortransmitting an analog audio signal to an audio transducer in accordancewith another aspect of the disclosure.

FIG. 4 illustrates a schematic diagram of another example apparatus fortransmitting an analog audio signal to an audio transducer in accordancewith another aspect of the disclosure.

FIG. 5 illustrates a schematic diagram of an example voltage scalingcircuit in accordance with another aspect of the disclosure.

FIG. 6 illustrates a schematic diagram of an example voltage summer andscaling circuit in accordance with another aspect of the disclosure.

FIG. 7 illustrates a flow diagram of an example method of transmittingan audio signal to an audio transducer in accordance with another aspectof the disclosure.

FIG. 8 illustrates a block diagram of an example wireless communicationdevice in accordance with another aspect of the disclosure.

FIGS. 9A-9C illustrate schematic diagrams of exemplary gate drivecircuits in accordance with other aspects of the disclosure.

DETAILED DESCRIPTION

The detailed description set forth below, in connection with theappended drawings, is intended as a description of variousconfigurations and is not intended to represent the only configurationsin which the concepts described herein may be practiced. The detaileddescription includes specific details for the purpose of providing athorough understanding of the various concepts. However, it will beapparent to those skilled in the art that these concepts may bepracticed without these specific details. In some instances, well-knownstructures and components are shown in block diagram form in order toavoid obscuring such concepts.

FIG. 1 illustrates a block/schematic diagram of an example apparatus 100for transmitting different types of data via one or more common nodes inaccordance with an aspect of the disclosure. In this example, thedifferent types of data include Universal Serial Bus (USB) digital datasignal and analog audio signal. However, it shall be understood that theconcepts described herein may be used with respect to other types ofsignals.

The apparatus 100 includes an integrated circuit (IC) 110, which may beconfigured as a system on chip (SOC) or other type of IC. The IC 110includes an application processor (AP) 120 configured to generate a USBdifferential data signal including a negative differential component USB(DN) and positive differential component USB (DP), where “D” stands fordata, and “N” and “P” stand for negative and positive, respectively. TheIC 110 further includes an audio codec 130 configured to generate ananalog audio signal AUD (R) and AUD (L), where “R” represents theright-channel signal component and “L” represents the left-channelsignal component.

The apparatus 100 further includes a USB port 150, such as a USB-C portor may be another version or type of port. A USB device (e.g., a USBflash drive) may be connected to the USB port 150 to receive the USBdifferential data signal USB (DN) and USB (DP) for storage and/or otherpurposes depending on the type of USB device. An audio device, such asan audio transducer like a headphone or speaker, may also be connectedto the USB port 150 to receive the analog audio signal AUD (R) and AUD(L). Although not shown, the apparatus 100 may include a device detectorconfigured to determine whether the device connected to the USB port 150is of the type to receive the USB differential data signal USB (DN) andUSB (DP) or an audio device to receive the analog audio signal AUD (R)and AUD (L).

The outputs of the AP 120 and audio codec 130 may connect to commonnodes or pads 142, 144, and 146 (e.g., off-chip pads on a printedcircuit board (PCB)). For example, the outputs USB (DN) and the AUD (R)associated with the AP 120 and audio codec 130 may connect to commonnode or pad 142, respectively. The outputs USB (DP) and the AUD (L)associated with the AP 120 and audio codec 130 may connect to commonnode or pad 144, respectively. The IC 110 may include a ground or returncoupled to a node or pad 146. The apparatus 100 may further includeswitching devices SW1, SW2, and SW3 connected between the nodes or pads142, 144, and 146, and DN, DP, and sideband use (SBU) 1/2 terminals ofthe USB port 150, respectively.

One of the challenges of the apparatus 100 is that different types ofdata share the common nodes or pads 142, 144, and 146 including theswitching devices SW1-SW3, respectively. For example, the USBdifferential data signal USB (DN) and USB (DP) may have a data rate orfrequency bandwidth (e.g., up to 10 gigabits per second (Gbps)) muchhigher than the analog audio signal AUD (R) and AUD (L) (e.g., 48kilobits per second (Kbps)). The analog audio signal AUD (R) and AUD (L)may include a total harmonic distortion (THD) of up to 110 or 120 dB.

The difference in the USB differential data signal and the analog audiosignal provides competing characteristics of the switching devices SW1to SW3 through which these signals propagate. For example, therelatively high data rate of the USB differential data signal suggeststhat the switching devices SW1-SW3 be made relatively small to keep thecapacitances of these devices small, so they do not impact the USBdifferential data signal. However, the analog audio signal requiresrelatively high THDs, which suggests that the switching devices SW1-SW3be made relatively large to handle the relatively high power of theanalog audio signal. For example, the terminals of the switching devicesSW1-SW3 may be required to handle up to 20 Volts.

FIG. 2 illustrates a block/schematic diagram of another exampleapparatus 200 for transmitting different types of data via one or morecommon nodes in accordance with another aspect of the disclosure. Theapparatus 200 may be an example more detailed implementation of theapparatus 100 previously discussed.

For example, the IC 110 may include audio amplifiers 210 and 220, and aset of switching devices SWA-SWE. The audio amplifier 210 is configuredto receive the right-channel audio signal AUD (R), and the audioamplifier 220 is configured to receive the left-channel audio signal(L). The switching devices SWA-SWB are coupled between the USB (DN) andUSB (DP) outputs of an application processor (AP), and nodes or pads 242and 244, respectively. The switching devices SWC and SWD are coupledbetween outputs of the audio amplifiers 210 and 220 and nodes or pads242 and 244, respectively. The switching device SWE is coupled betweenground and node or pad 246. The application processor (AP) may controlthe states (open/closed) of the set of switching devices SWA-SWE. Theremaining circuitry of the apparatus 200 may be substantially the sameas that of apparatus 100. That is, the apparatus 200 also includes theset of switching devices SW1-SW3 coupled between the nodes or pads 242,244, and 246, and DN, DP, and SBU1/2 terminals of the USB port 250,respectively.

If the apparatus 200 detects a device connected to the USB port 250 thatis to receive the USB differential data signal, the applicationprocessor (AP) closes switching devices SWA, SWB, SWE, and SW1-SW3, andopens SWC and SWD. In this configuration, the USB differential datasignal USB (DN) and USB (DP) is sent to the device via switching devicesSWA/SW1 and SWB/SW2, and the return USB differential data signal isgrounded via SW3/SWE. If the apparatus 200 detects a device connected tothe USB port 250 that is to receive the analog audio signal, theapplication processor (AP) closes switching devices SWC, SWD, SWE, andSW1-SW3, and opens SWA and SWB. In this configuration, the analog audiosignal AUD (R) and AUD (L) is sent to the device via switching devicesSWC/SW1 and SWD/SW2, and the return USB differential data signal isgrounded via SW3/SWE.

The same issues that were discussed above with respect to the sameswitching devices SW1-SW3 of apparatus 100 still apply. That is, for therelatively high data rates of the USB differential data signal, theswitching devices SW1-SW3 should be made relatively small to keep thecapacitances low associated with these devices so they do not adverselyimpact the USB differential data signal. To handle the THD requirementsof the analog audio signal, the switching devices SW1-SW3 should be maderelatively large to handle the relatively high power/voltage of theanalog audio signal.

FIG. 3 illustrates a schematic diagram of an example apparatus 300 fortransmitting an analog audio signal to an audio transducer in accordancewith another aspect of the disclosure. In summary, the set of switchingdevices SW1-SW3 are configured as field effect transistors (FETs), suchas n-channel metal oxide semiconductor field effect transistors (NMOSFETs). Further, the apparatus 300 includes gate drive circuitsconfigured to provide gate voltages to the switching FETs SW1-SW3 suchthat they are operated in a more linear manner to reduce the THD of theanalog audio signal. This allows the use of relatively small switchingFETs SW1-SW3 so as not to significantly impact the USB differential datasignal, while linearizing the operations of the switching FETs SW1-SW3so they can handle the analog audio signal.

More specifically, the apparatus 300 includes a first audio amplifier310, a first gate drive circuit 350, and a first switching FET SW1. Theapparatus 300 further includes a second audio amplifier 320, a secondgate drive circuit 360, and a second switching FET SW2. Additionally,the apparatus 300 includes a third gate drive circuit 370 and a thirdswitching FET SW3. A first audio load R_(L)(R), such as a right-channelaudio transducer (e.g., a headphone, earpiece or speaker), is coupled orconnected between the first switching FET SW1 and the third switchingFET SW3. A second audio load R_(L)(L), such as a left-channel audiotransducer (e.g., a headphone, earpiece or speaker), is coupled orconnected between the second switching FET SW2 and the third switchingFET SW3.

The first audio amplifier 310 includes an input configured to receive aright-channel analog audio signal AUD (R), and amplify the analog audiosignal AUD (R) to generate an output voltage VinR. The first gate drivecircuit 350 includes a first voltage scaling device 352 and a firstvoltage summer 354. The first voltage scaling device 352 includes aninput coupled to the output of the first audio amplifier 310, and isconfigured to scale the output voltage VinR by a scaling factor β. Thefirst voltage summer 354 includes a first input coupled to an output ofthe first voltage scaling device 352, a second input configured toreceive a direct current (DC) voltage VDCR, and an output configured toproduce a first gate voltage VGR for the gate of the first switching FETSW1. Thus, the first gate voltage VGR may be represented by thefollowing equation:VGR=VinR*β+VDCR  Eq. 1

The first audio amplifier 310 and/or the first gate drive circuit 350may be part of an integrated circuit (IC) or dedicated circuitry. Thefirst switching FET SW1 includes a source (and bulk) coupled to theoutput of the first audio amplifier 310 via node or pad 342, a gatecoupled to the output of the first gate drive circuit 350, and a draincoupled to a first terminal of the right-channel audio load R_(L)(R).

The second audio amplifier 320 includes an input configured to receive aleft-channel analog audio signal AUD (L), and amplify the analog audiosignal AUD (L) to generate an output voltage VinL. The second gate drivecircuit 350 includes a second voltage scaling device 362 and a secondvoltage summer 364. The second voltage scaling device 362 includes aninput coupled to the output of the second audio amplifier 320, and isconfigured to scale the output voltage VinL by a scaling factor α. Thesecond voltage summer 364 includes a first input coupled to an output ofthe second voltage scaling device 362, a second input configured toreceive a DC voltage VDCL, and an output configured to produce a secondgate voltage VGL for the gate of the second switching FET SW2. Thus, thesecond gate voltage VGL may be represented by the following equation:VGL=VinL*α+VDCL  Eq. 2

The second audio amplifier 320 and/or the second gate drive circuit 360may be part of an integrated circuit (IC) or dedicated circuitry. Thesecond switching FET SW2 includes a source (and bulk) coupled to theoutput of the second audio amplifier 320 via node or pad 344, a gatecoupled to the output of the second gate drive circuit 360, and a draincoupled to a first terminal of the left-channel audio load R_(L)(L).

The third gate drive circuit 370 includes a third voltage summer 372, athird voltage scaling device 374 and a fourth voltage summer 376. Thethird voltage summer 372 includes first and second inputs coupled to theoutputs of the first and second audio amplifiers 310 and 320,respectively. Accordingly, the third voltage summer 372 is configured tosum the output voltages VinR and VinL of the first and second audioamplifiers 310 and 320, respectively. The third voltage scaling device374 includes an input coupled to the output of the third voltage summer372, and is configured to scale the sum of the output voltage VinR+VinLby a scaling factor γ. The fourth voltage summer 376 includes a firstinput coupled to an output of the third voltage scaling device 374, asecond input configured to receive a DC voltage VDC0, and an outputconfigured to produce a third gate voltage VG0 for the gate of the thirdswitching FET SW3. Thus, the third gate voltage VG0 may be representedby the following equation:VG0=(VinR+VinL)*γ+VDC0  Eq. 3

The third gate drive circuit 370 may be part of an integrated circuit(IC) or dedicated circuitry. The third switching FET SW1 includes asource (and bulk) coupled to ground via node or pad 346, a gate coupledto the output of the third gate drive circuit 370, and a drain coupledto respective second terminals of the right- and left-channel audioloads R_(L)(R) and R_(L)(L).

The linearization of the switching FETs SW1-SW3 operates as follows: Ifthe switching FETs SW1-SW3 were to be operated by a constant gatevoltage, the resistances of the FETs would vary with the audio voltagesVinR, VinL, and VinR+VinL because their respective gate-to-sourcevoltages vary with these voltages VinR, VinL, and VinR+VinL,respectively. The variation of the voltage in combination with thevariation of the FET resistance produces a non-linear response thatincreases the THD of the analog audio signal. However, the gate drivecircuits 350, 360, and 370 generate gate voltages VGR, VGL, and VG0 thatvaries proportionally with the input voltages VinR, VinL, and VinR+VinLin accordance with equations 1-3, respectively. Since the gate voltageand the source voltage varying in a similar manner, the gate-to-sourcevoltages of the FETs SW1-SW3 remain substantially constant; andconsequently, the FET resistance remain substantially constant. Thisresults in a more linearized response of the switching FETs SW1-SW3;thereby, allowing the FETs to be made smaller for USB differential datapurposes, and reducing the THD for analog audio signal purpose.

The DC voltages VDCR, VDCL, and VDC0 applied to the gates of theswitching FETs SW1-SW3 as indicated in equations 1-3 are to keep theswitching FETs SW1-SW3 minimally turned on or turned on to a certaindegree, while the proportional components β*VinR, α*VinL, andγ*(VinR+VinL) drive the switching FETs SW1-SW3 harder in proportion tothe voltages VinR, VinL, and (VinR+VinL) to produce a more linearizedresponse from the switching FETs SW1-SW3, respectively.

FIG. 4 illustrates a schematic diagram of another example apparatus 400for transmitting an analog audio signal to an audio transducer inaccordance with another aspect of the disclosure. The apparatus 400 issimilar to that of apparatus 300, and includes many of the sameelements, such as first and second audio amplifiers 410 and 420, a setof switching FETs SW1-SW3, a set of gate drive circuits 450, 460, and470 including voltage scaling devices 452, 462, and 474, summers 454,464, and 476, and additional summer 474 in the case of gate drivecircuit 470. The configuration and operation of these elements have beendescribed with reference to the same elements in apparatus 300, whichare identified with the same reference numbers with the exception thatthe most significant digit is a “4” in apparatus 400 instead of a “3” inapparatus 300.

The apparatus 400 further includes a set of bulk bias circuits 456, 466,and 480 configured to generate bulk voltages VBR, VBL, and VB0 for theset of switching FETs SW1-SW3, respectively. Accordingly, the set ofbulk bias circuits 456, 466, and 480 include a set of outputs (at whichthe bulk voltages VBR, VBL, and VB0 are generated) coupled to the bulksof the set of switching FETs SW1-SW3, respectively. Note that the bulksof the switching FETs SW1-SW3 in apparatus 400 are not coupled to thecorresponding sources of the FETs SW1-SW3, respectively.

The bulk bias circuit 456 is configured as a voltage scaling deviceconfigured to scale the voltage VinR at the output of the first audioamplifier 410 by a factor ν to generate the bulk voltage VBR for theswitching FET SW1. The bulk bias circuit 466 is configured as a voltagescaling device configured to scale the voltage VinL at the output of thesecond audio amplifier 420 by a factor μ to generate the bulk voltageVBL for the switching FET SW2. The bulk bias circuit 480 includes avoltage summer 482 including inputs coupled to the outputs of the firstand second audio amplifiers 410 and 420, respectively. Accordingly, thevoltage summer 482 is configured to sum the voltages VinR and VinL atthe outputs of the first and second audio amplifiers 410 and 420,respectively. The bulk bias circuit 480 further includes a voltagescaling device 484 configured to scale the sum of the voltages VinR andVinL by a factor χ to generate the bulk voltage VB0 for the switchingFET SW3.

The bulk bias circuits 456, 466, and 480 are particularly useful whenthe output voltages VinR, VinL, and VinR+VinL swing between positive andnegative voltages. The scaling factors ν, μ, and χ may be configured toset the bulk voltages VBR, VBL, and VB0 substantially around the middleof the voltage swing of the voltages VinR, VinL, and VinR+VinL,respectively. In such case, the drain-to-bulk voltage and thesource-to-bulk voltage swing between similar voltage ranges. Thus, theswitching FETs SW1-SW3 are operated more symmetrical.

FIG. 5 illustrates a schematic diagram of an example voltage scalingcircuit 500 in accordance with another aspect of the disclosure. Thevoltage scaling circuit 500 may be an example of any of the voltagescaling circuits 352, 362, 452, 456, 462, and 466 previously discussed.The voltage scaling circuit 500 is also shown with a corresponding audioamplifier 510, which may correspond to any of the audio amplifiers 310,320, 410, and 420 previously discussed.

The voltage scaling circuit 500 includes a difference amplifier 520, afirst resistor R₁, and a second resistor R₂, which may be variable. Thefirst and second resistors R₁ and R₂ are coupled or connected in seriesbetween the output of the audio amplifier 510 and a voltage rail (e.g.,ground). The difference amplifier 520 includes a first input (e.g., apositive input) coupled to the output of the audio amplifier 510, and asecond input (e.g., a negative input) coupled to a node between thefirst and second resistors R₁ and R₂. A control signal Vctrl1<N:1>controls the net resistance of the variable resistor R₂ between thenegative input of the difference amplifier 520 and the voltage rail. IfR_(T) is the total resistance of the variable resistor R₂, and R₂ isalso the net resistance of the variable resistor R₂, then the netresistance R₂ may be determined by the following equation:R ₂ =R _(T)*(2^(<N:1>)/2^(N))  Eq. 4

Where <N:1> is the digital value of the control signal Vctrl1<N:1>.Assuming the difference amplifier 520 has a unity gain, the differenceamplifier 520 includes an output configured to produce a scaled voltageVs in accordance with the following equation:

$\begin{matrix}{V_{S} = {\left( \frac{R_{1}}{R_{1} + R_{2}} \right){Vin}}} & {{Eq}.5}\end{matrix}$

Where R₁ is the resistance of the resistor R₁. Thus, byselecting/adjusting the resistances R₁ and R₂ corresponding to thevoltage scaling circuits 352/452, 362/462, 456, and 466, the scalingfactors β, α, ν, and μ may be set.

FIG. 6 illustrates a schematic diagram of an example voltage summer andscaling circuit 600 in accordance with another aspect of the disclosure.The voltage summer and scaling circuit 600 may be an example of aseries-connected voltage summer and voltage scaling circuit, suchsummers-voltage scaling circuits 372-374, 472-474, and 482-484previously discussed.

The voltage summer and scaling circuit 600 includes a summing amplifier610 including inputs configured to receive the output voltages VinR andVinL from the outputs of the first and second audio amplifiers 310/410and 320/420, respectively. Assuming the summing amplifier 610 has unitygain, the summing amplifier 610 is configured to generate the sum of thevoltages VinR+VinL. The voltage summer and scaling circuit 600 furtherincludes a difference amplifier 620, a first resistor R₃, and a secondresistor R₄, which may be variable. The first and second resistors R₃and R₄ are coupled or connected in series between the output of thesumming amplifier 610 and a voltage rail (e.g., ground). The differenceamplifier 620 includes a first input (e.g., a positive input) coupled tothe output of the summing amplifier 610, and a second input (e.g., anegative input) coupled to a node between the first and second resistorsR₃ and R₄. A control signal Vctrl2<N:1> controls the net resistance ofthe variable resistor R₄ between the negative input of the differenceamplifier 620 and the voltage rail. If R_(T) is the total resistance ofthe variable resistor R₄, and R₄ is also the net resistance of thevariable resistor R₄, then the net resistance R₄ may be determined bythe following equation:R ₄ =R _(T)*(2^(<N:1>)/2^(N))  Eq. 6

Where <N:1> is the digital value of the control signal Vctrl2<N:1>.Assuming the difference amplifier 620 has a unity gain, the differenceamplifier 620 includes an output configured to produce a scaled voltageVs in accordance with the following equation:

$\begin{matrix}{V_{S} = {\left( \frac{R_{3}}{R_{3} + R_{4}} \right)\left( {{{Vin}R} + {{Vin}L}} \right)}} & {{Eq}.7}\end{matrix}$

Where R₃ is the resistance of the resistor R₃. Thus, byselecting/adjusting the resistances R₃ and R₄ corresponding to thevoltage scaling circuits 374/474 and 484, the scaling factors γ and χmay be set.

FIG. 7 illustrates a flow diagram of an example method 700 fortransmitting an audio signal to an audio transducer in accordance withanother aspect of the disclosure. The method 700 includes amplifying afirst audio signal using a first audio amplifier to generate a firstvoltage (block 710). Examples of means for amplifying a first audiosignal using a first audio amplifier to generate a first voltage any ofthe audio amplifiers 310, 320, 410, and 420 previously discussed.

The method 700 further includes generating a first gate voltage based onthe first voltage (block 720). Examples of means for generating a firstgate voltage based on the first voltage include any of the gate drivecircuits 350, 360, 450, 460, and 500 previously discussed.

The method 700 additionally includes applying the first gate voltage toa first gate of a first field effect transistor (FET) coupled betweenthe first audio amplifier and a first audio transducer (block 730).Examples of means for applying the first gate voltage to a first gate ofa first field effect transistor (FET) coupled between the first audioamplifier and a first audio transducer include the coupling of the gatedrive circuits 350, 360, 450, 460, and 500 to the gate of thecorresponding FETs SW1 and SW2.

The method 700 also includes applying the first voltage to a firstsource of the first FET. Examples of means for applying the firstvoltage to a first source of the first FET include the coupling of theoutputs of the amplifiers 310, 320, 410, and 420 to the sources of FETsSW1 and SW2.

The generating of the first gate voltage as specified in block 720 mayinclude scaling the first voltage by a first scaling factor to generatea first scaled voltage, and summing the first scaled voltage with afirst direct current (DC) voltage to generate the first gate voltage.Examples of means for scaling the first voltage by a first scalingfactor to generate a first scaled voltage include any of the voltagescaling circuits 352, 362, 374, 452, 464, and 474. Examples of means forsumming the first scaled voltage with a first direct current (DC)voltage to generate the first gate voltage include any of the voltagesummers 354, 364, 376, 454, 464, and 476.

The method 700 may further include amplifying a second audio signalusing a second audio amplifier to generate a second voltage; generatinga second gate voltage based on the second voltage; applying the secondgate voltage to a second gate of a second field effect transistor (FET)coupled between the second audio amplifier and a second audiotransducer; and applying the second voltage to a second source of thesecond FET. The means for performing these operations have beenpreviously discussed with reference to blocks 710, 720, 730, and 740.

The method 700 may further include generating a third gate voltage basedon a sum of the first and second voltages, and applying the third gatevoltage to a third gate of a third field effect transistor (FET) coupledbetween the first and second audio transducers and a voltage rail.Examples of means for generating a third gate voltage based on a sum ofthe first and second voltages include any of the first voltage summers372 and 472, voltage scaling devices 374 and 474, and second voltagesummers 376 and 476. Examples of means for applying the third gatevoltage to a third gate of a third field effect transistor (FET) coupledbetween the first and second audio transducers and a voltage railinclude the coupling of the outputs of the gate drive circuits 370 and470 to the gates of the switching FET SW3.

Additionally, the method 700 may include generating a first bulk voltagebased on the first voltage, applying the first bulk voltage to a firstbulk of the first FET, generating a second bulk voltage based on thesecond voltage, applying the second bulk voltage to a second bulk of thesecond FET, generating a third bulk voltage based on a sum of the firstand second voltages, and applying the third bulk voltage to a third bulkof the third FET.

Example of means for generating a first bulk voltage based on the firstvoltage includes bulk bias circuit 456. Example of means for applyingthe first bulk voltage to a first bulk of the first FET includes thecoupling of the output of the bulk bias circuit 456 to the bulk ofswitching FET SW1. Example of means for generating a second bulk voltagebased on the second voltage includes bulk bias circuit 466. Example ofmeans for applying the second bulk voltage to a second bulk of thesecond FET includes the coupling of the output of the bulk bias circuit466 to the bulk of switching FET SW2. Example of means for generating athird bulk voltage based on a sum of the first and second voltagesincludes bulk bias circuit 480. Example of means for applying the thirdbulk voltage to a third bulk of the third FET includes the coupling ofthe bulk bias circuit 480 to the bulk of the switching FET SW3.

FIG. 8 illustrates a block diagram of an example wireless communicationdevice 800 in accordance with another aspect of the disclosure. Thewireless communication device 800 includes at least one antenna 860(e.g., at least one antenna array), a transceiver 850, and an integratedcircuit (IC) 805, which may be configured as a system on chip (SOC). TheSOC 805 includes one or more digital signal processing cores 810, anapplication processor 815, an audio codec 820, switching devicesSWA-SWF, and gate drive circuits GDC-R 825, GDC-L 830, and GDC-0 835.

The one or more digital signal processing cores 810 may be configured toprocess data to generate a baseband (BB) signal, the transceiver 850 maybe configured to process the baseband (BB) signal received from the oneor more digital signal processing cores 810 to generate a radiofrequency (RF) signal. The at least one antenna 860 may be configured toradiate the RF signal for wireless transmission to one or more remotedevices. Similarly, the at least one antenna 860 is configured toreceive an RF signal from a remote device, the transceiver 850 may beconfigured to process the RF signal received from the at least oneantenna 860 to generate a baseband (BB) signal. The one or more digitalsignal processing cores 810 may be configured to process the baseband(BB) signal to extract data therefrom.

In USB mode, the application processor 815 may receive data from the oneor more digital signal processing cores 810, and generate a USBdifferential data signal USB (DN) and USB (DP). The applicationprocessor 815 may provide the USB differential data signal USB (DN) andUSB (DP) to the sources of switching FETs SW1-SW2 via closed switchingdevices SWA-SWB controlled by a mode select signal generated by theapplication processor 815, respectively. Also, in USB mode, theapplication processor 815 may receive the USB differential data signalUSB (DN) and USB (DP) via the turned-on switching FETs SW1-SW2 andclosed switching devices SWA-SWB, respectively, and provide data basedon the received USB differential data signal to the one or more digitalsignal processing cores 810.

In audio mode, the audio codec 820 may receive data from the one or moredigital signal processing cores 810, and generate an analog audio signalAUD (R) and AUD (L). The audio codec may provide the analog audio signalAUD (R) and AUD (L) to the sources of switching FETs SW1-SW2 via closedSWC-SWD controlled by the mode select signal, respectively. The gatedrive circuits (GDC-R) 825 and GDC-L 830 are configured to generate gatevoltages for the switching FETs SW1-SW2 proportional to the voltagesVinR and VinL at the outputs AUD (R) and AUD (L) in audio mode,respectively.

The switching FET SW3 provides a ground or return for audio transducers870-R and 870-L connected to a USB port 840. The apparatus 800 includesa gate drive circuit (GDC-0) 835 configured to generate a gate voltagefor the switching FET SW3 proportional to a sum of the voltagesVinR+VinL at the outputs AUD (R) and AUD (L) in audio mode. Groundpotential may be applied to the source of switching device SW3 and aheadphone reference (HPF REF) input of the audio codec 820 via closedswitching device SWF and/or SWE. The drains of the switching devicesFETs SW1-SW3 are coupled to the DN, DP, and SBU1/2 terminals of the USBport 840; and when the audio transducers 870-R and 870-L is connected tothe USB ports, the positive terminals and the common return of the audiotransducers 870-R and 870-L are coupled to the DN, DP, and SBU1/2terminals of the USB port 840, respectively. Alternatively, a USBdigital data device (e.g., USB memory device, keyboard, mouse, etc.) maybe connected to the USB port 840 instead of the audio transducers. InUSB mode, the switching device SWF may be closed.

FIG. 9A illustrates a schematic diagram of an exemplary gate drivecircuit 900 in accordance with another aspect of the disclosure. Thegate drive circuit 900 may be an example of a more detailedimplementation of gate drive circuit GDC-R 825 previously discussed. Thegate drive circuit 900 includes an audio-mode gate drive subcircuit 910including a voltage scaling (P) device 912 including an input coupled toan output of the AUD(R) output of the audio codec 820, and configured toreceive an input voltage VinR; and a summer 914 including a first inputcoupled to an output of the voltage scaling device 912, a second inputconfigured to receive a DC voltage VDCR, and an output configured togenerate an audio-mode gate voltage AUD VGR for the first switching FETSW1.

The gate drive circuit 900 may further include a USB-mode gate voltageVGR generator 916 configured to generate a USB-mode gate voltage USB VGRto maintain the first switching FET SW1 turned on in USB mode. The gatedrive circuit 900 further includes a multiplexer 920 including a firstinput coupled to the output of the audio-mode gate drive subcircuit 910,a second input coupled to the output of the USB gate voltage generator916, a select input configured to receive the mode select signal fromthe application processor 815, and an output configured to produce agate voltage VGR for the first switching FET SW1. Thus, if the modeselect signal indicates audio mode, the multiplexer 920 outputs theaudio-mode gate voltage AUD VGR as the gate voltage VGR for the firstswitching FET SW1. If the mode select signal indicates USB mode, themultiplexer 920 outputs the USB-mode gate voltage USB VGR as the gatevoltage VGR for the first switching FET SW1.

FIG. 9B illustrates a schematic diagram of another exemplary gate drivecircuit 930 in accordance with another aspect of the disclosure. Thegate drive circuit 930 may be an example of a more detailedimplementation of gate drive circuit GDC-L 830 previously discussed. Thegate drive circuit 930 includes an audio-mode gate drive subcircuit 940including a voltage scaling (a) device 912 including an input coupled toan output of the AUD(L) output of the audio codec 820, and configured toreceive an input voltage VinL; and a summer 944 including a first inputcoupled to an output of the voltage scaling device 942, a second inputconfigured to receive a DC voltage VDCL, and an output configured togenerate an audio-mode gate voltage AUD VGL for the second switching FETSW2.

The gate drive circuit 930 may further include a USB-mode gate voltageVGL generator 946 configured to generate a USB-mode gate voltage USB VGLto maintain the second switching FET SW2 turned on in USB mode. The gatedrive circuit 930 further includes a multiplexer 950 including a firstinput coupled to the output of the audio-mode gate drive subcircuit 940,a second input coupled to the output of the USB gate voltage generator946, a select input configured to receive the mode select signal fromthe application processor 815, and an output configured to produce agate voltage VGL for the second switching FET SW2. Thus, if the modeselect signal indicates audio mode, the multiplexer 950 outputs theaudio-mode gate voltage AUD VGL as the gate voltage VGL for the secondswitching FET SW2. If the mode select signal indicates USB mode, themultiplexer 950 outputs the USB-mode gate voltage USB VGL as the gatevoltage VGL for the second switching FET SW2.

FIG. 9C illustrates a schematic diagram of another exemplary gate drivecircuit 960 in accordance with another aspect of the disclosure. Thegate drive circuit 960 may be an example of a more detailedimplementation of gate drive circuit GDC-0 835 previously discussed. Thegate drive circuit 960 includes an audio-mode gate drive subcircuit 970including a first summer 972 including inputs coupled to the AUD(R) andAUD(L) outputs of the audio codec 820; a voltage scaling (γ) device 974including an input coupled to an output of the first summer 972; and asecond summer 976 including a first input coupled to an output of thevoltage scaling device 974, a second input configured to receive a DCvoltage VDC0, and an output configured to generate an audio-mode gatevoltage AUD VG0 for the third switching FET SW3.

The gate drive circuit 960 may further include a USB-mode gate voltageVG0 generator 978 configured to generate a USB-mode gate voltage USB VG0to maintain the third switching FET SW3 turned on in USB mode. The gatedrive circuit 960 further includes a multiplexer 980 including a firstinput coupled to the output of the audio-mode gate drive subcircuit 970,a second input coupled to the output of the USB gate voltage generator978, a select input configured to receive the mode select signal fromthe application processor 815, and an output configured to produce agate voltage VG0 for the third switching FET SW3. Thus, if the modeselect signal indicates audio mode, the multiplexer 980 outputs theaudio-mode gate voltage AUD VG0 as the gate voltage VG0 for the thirdswitching FET SW3. If the mode select signal indicates USB mode, themultiplexer 980 outputs the USB-mode gate voltage USB VG0 as the gatevoltage VG0 for the third switching FET SW3.

The previous description of the disclosure is provided to enable anyperson skilled in the art to make or use the disclosure. Variousmodifications to the disclosure will be readily apparent to thoseskilled in the art, and the generic principles defined herein may beapplied to other variations without departing from the spirit or scopeof the disclosure. Thus, the disclosure is not intended to be limited tothe examples described herein but is to be accorded the widest scopeconsistent with the principles and novel features disclosed herein.

What is claimed:
 1. An apparatus, comprising: a first amplifier; a first field effect transistor (FET) including a first source coupled to an output of the first amplifier, and a first drain for coupling to a first load; and a first gate drive circuit including an input coupled to the output of the first amplifier and an output coupled to a first gate of the first FET.
 2. The apparatus of claim 1, wherein the first gate drive circuit comprises a voltage scaling device including an input coupled to the output of the first amplifier.
 3. The apparatus of claim 1, wherein the first gate drive circuit comprises: a voltage scaling device including an input coupled to the output of the first amplifier; and a voltage summer including a first input coupled to an output of the voltage scaling device, a second input configured to receive a direct current (DC) voltage, and an output coupled to the first gate of the first FET.
 4. The apparatus of claim 3, wherein the voltage scaling device comprises: first and second resistors coupled in series between the output of the first amplifier and a voltage rail; and a difference amplifier including a first input coupled to the output of the first amplifier, a second input coupled to a node between the first and second resistors, and an output coupled to the first gate of the first FET.
 5. The apparatus of claim 1, wherein the first amplifier comprises an input configured to receive an analog audio signal.
 6. The apparatus of claim 1, wherein the first load comprises an audio transducer.
 7. The apparatus of claim 1, further comprising a Universal Serial Bus (USB) port coupled between the first FET and the first load.
 8. The apparatus of claim 1, further comprising: a second amplifier; a second field effect transistor (FET) including a second source coupled to an output of the second amplifier, and a second drain for coupling to a second load; and a second gate drive circuit including an input coupled to the output of the second amplifier and an output coupled to a second gate of the second FET.
 9. The apparatus of claim 8, wherein the second gate drive circuit comprises a voltage scaling device including an input coupled to the output of the second amplifier.
 10. The apparatus of claim 8, wherein the second gate drive circuit comprises: a voltage scaling device including an input coupled to the output of the second amplifier; and a voltage summer including a first input coupled to an output of the voltage scaling device, a second input configured to receive a direct current (DC) voltage, and an output coupled to the second gate of the second FET.
 11. The apparatus of claim 8, further comprising: a third field effect transistor (FET) including a third source coupled to a voltage rail, and a third drain for coupling to the first and second loads; and a third gate drive circuit including a first input coupled to the output of the first amplifier, a second input coupled to the output of the second amplifier, and an output coupled to a third gate of the third FET.
 12. The apparatus of claim 11, wherein the third gate drive circuit comprises: a first voltage summer including a first input coupled to the output of the first amplifier, and a second input coupled to the output of the second amplifier; a voltage scaling device including an input coupled to the output of the first voltage summer; and a second voltage summer including a first input coupled to an output of the voltage scaling device, a second input configured to receive a direct current (DC) voltage, and an output coupled to the third gate of the third FET.
 13. The apparatus of claim 12, wherein the first voltage summer comprises a summing amplifier including a first input coupled to the output of the first amplifier, and a second input coupled to the output of the second amplifier, and wherein the voltage scaling device comprises: first and second resistors coupled in series between an output of the summing amplifier and a voltage rail; and a difference amplifier including a first input coupled to the output of the summing amplifier, a second input coupled to a node between the first and second resistors, and an output coupled to the third gate of the third FET.
 14. The apparatus of claim 1, further comprising a first bulk drive circuit including an input coupled to the output of the first amplifier, and an output coupled to a first bulk of the first FET.
 15. The apparatus of claim 14, wherein the first bulk drive circuit comprises a voltage scaling device.
 16. The apparatus of claim 14, further comprising: a second amplifier; a second field effect transistor (FET) including a second source coupled to an output of the second amplifier, and a second drain for coupling to a second load; and a second gate drive circuit including an input coupled to the output of the second amplifier and an output coupled to a second gate of the second FET.
 17. The apparatus of claim 16, further comprising a second bulk drive circuit including an input coupled to the output of the second amplifier, and an output coupled to a second bulk of the second FET.
 18. The apparatus of claim 17, wherein the second bulk drive circuit comprises a voltage scaling device.
 19. The apparatus of claim 17, further comprising: a third field effect transistor (FET) including a third source coupled to a voltage rail, and a third drain for coupling to the first and second loads; and a third gate drive circuit including a first input coupled to the output of the first amplifier, a second input coupled to the output of the second amplifier, and an output coupled to a third gate of the third FET.
 20. The apparatus of claim 19, further comprising a third bulk drive circuit including a first input coupled to the output of the first amplifier, a second input coupled to the output of the second amplifier, and an output coupled to a third bulk of the third FET.
 21. The apparatus of claim 20, wherein the third bulk drive circuit comprises: a voltage summer including a first input coupled to the output of the first amplifier, and a second input coupled to the output of the second amplifier; and a voltage scaling device including an input coupled to an output of the voltage summer, and an output coupled to the third bulk of the third FET.
 22. A method, comprising: amplifying a first audio signal using a first audio amplifier to generate a first voltage; generating a first gate voltage based on the first voltage, wherein generating the first gate voltage comprises: scaling the first voltage by a first scaling factor to generate a first scaled voltage; and summing the first scaled voltage with a first direct current (DC) voltage to generate the first gate voltage; and applying the first gate voltage to a first gate of a first field effect transistor (FET) coupled between the first audio amplifier and a first audio transducer.
 23. The method of claim 22, further comprising: amplifying a second audio signal using a second audio amplifier to generate a second voltage; generating a second gate voltage based on the second voltage; and applying the second gate voltage to a second gate of a second field effect transistor (FET) coupled between the second audio amplifier and a second audio transducer.
 24. The method of claim 23, further comprising: generating a third gate voltage based on a sum of the first and second voltages; and applying the third gate voltage to a third gate of a third field effect transistor (FET) coupled between the first and second audio transducers and a voltage rail.
 25. The method of claim 24, further comprising: generating a first bulk voltage based on the first voltage; applying the first bulk voltage to a first bulk of the first FET; generating a second bulk voltage based on the second voltage; applying the second bulk voltage to a second bulk of the second FET; generating a third bulk voltage based on a sum of the first and second voltages; and applying the third bulk voltage to a third bulk of the third FET.
 26. An apparatus, comprising: means for amplifying a first audio signal using a first audio amplifier to generate a first voltage; means for generating a first gate voltage based on the first voltage; and means for applying the first gate voltage to a first gate of a first field effect transistor (FET) coupled between the first audio amplifier and a first audio transducer.
 27. The apparatus of claim 26, further comprising: means for amplifying a second audio signal using a second audio amplifier to generate a second voltage; means for generating a second gate voltage based on the second voltage; means for applying the second gate voltage to a second gate of a second field effect transistor (FET) coupled between the second audio amplifier and a second audio transducer.
 28. The apparatus of claim 27, further comprising: means for generating a third gate voltage based on a sum of the first and second voltages; and means for applying the third gate voltage to a third gate of a third field effect transistor (FET) coupled between the first and second audio transducers and a voltage rail.
 29. A wireless communication device, comprising: at least one antenna; a transceiver coupled to the at least one antenna; at least one digital signal processing core coupled to the transceiver; a port configured to connect to one of at least one audio transducer and a digital data device; at least one audio amplifier; at least one field effect transistor (FET) including a source coupled to an output of the at least one audio amplifier, respectively, and a drain coupled to the port; and at least one gate drive circuit including an input coupled to the output of the at least one audio amplifier, and an output coupled to a gate of the at least one FET. 